A cured transparent rubber composition is a material which is tough while exhibiting rubber behavior and through which visible light passes, which for many applications is a desirable property. Applications wherein cured transparent rubber compositions may be used include, but not limited to, footwear products, tires, clothes, mask, rain gear, toys, damping materials, building components, coating material for wiring, packaging materials, protection members for computers, computer peripherals, contraceptive devices, sex toys, artificial nipples, disposable diapers, stationery, containers, food trays, balls for sports, ball chairs, protection films, seals, and key covers, shoe soles, medical stoppers and the like. Shoe soles and similar applications are of interest, provided the minimum requirements with respect to abrasion resistance are met.
Thus, a transparent shoe sole should be clear and transparent (i.e., total transmittance greater than 80%, with haze below 30%, both according to ASTM D1003-13), but also have strong mechanical properties, good UV stability, excellent shelf life as unvulcanized compound and have preferably an abrasion resistance (ISO 4649, method A) of less than 200 mm3.
In WO2008091847 a composition is described comprising at least one polyisoprene and at least one EAODM polymer. Said polymer has a good abrasion resistance and good tear resistance. Said rubber composition comprises 28.9 wt. % of natural rubber, 9.5 wt. % of polybutadiene, 12.4 wt. % of the EAODM, 24.8 wt. % of carbon black and 1.38 wt. % of a vulcanization system. Unfortunately, said system is not transparent. For the avoidance of doubt, the EAODM (NDR 46140) is not a polyalkenamer.
In JP2011110105 a shoe sole forming sheet is described that is useful for efficiently joining a crosslinked rubber layer as a stud and a thermoplastic elastomer layer as a sole. Paragraph 160 of the translated specification describes a Rubber composition 1 which comprises “50 parts by weight of crude rubber, and butadiene rubber (the Dow Chemical Co. make --) “Buna EM1500” 50 part by weight and polyoctenylene (the product made from EBONIKKU GmbH —) “BESUTENEMA 8012” 5 part by weight and clay (the product made from Hoffmann Mineral —) “Silitin Z86” 25 parts by weight, 45 parts by weight of carbon black (N335), 10 parts by weight of plasticizers (the product made from Bayer, “Vulcanol 88”), 1 part by weight of stearic acid, and a vulcanization active agent (the product made from Elaborate Chemicals, and “Hicross M”—)”. Said system, based on natural rubber and high amounts of additives, is not transparent.
(EP1932688) concerns a pneumatic run-flat tire. The elastomeric layers comprise a rubber composition comprising 100 parts by weight of natural rubber or synthetic rubber, 10-30 phr of silica and from 1 to 20 phr of polyoctenamer. Again, said composition is not transparent.
Excellent transparent rubber compositions have for instance been described in WO2014132718. Even though in this application an improved balance has been found between rubber properties such as hardness and strength on the one hand and transparency on the other hand, there is still a need for further improvement, in particular with respect to abrasion resistance. This requirement is particularly important for sport shoes, where lower abrasion resistance is required as compared to ordinary shoes (e.g., <120 mm3). Now a new composition has been found that can be used for shoe soles and other applications.